This invention relates to a mining auger used in particular for the underground mining of coal. It has a conically shaped frontal terminal body (hereafter "end ring") which has along its outer edge a plurality of peripherally distributed spaced cutting tool holders in which individual cutting tool bits are secured. The longitudinal axis of each cutting tool is oriented at an inclination to an imaginary frontal plane of the auger. This frontal plane is defined here as being oriented perpendicularly to the auger axis and touching the tips of each cutting tool bit. Thus, during operation of the mining auger, the thus defined frontal plane generally coincides with the face of the mine wall, assumed to extend perpendicularly to the auger axis. Further, the cutting tool bits project beyond the outer edge of the conical end ring.
Mining augers with single or multiple auger helices for the underground mining are generally known. They conventionally have a hollow auger shaft to the outer face of which a single auger helix or a plurality of auger helices are welded. To the edge zone of the helix, tool holders are welded at equal distances. Each tool holder carries a cutting tool bit. The end face of the mining auger oriented towards the mining wall is closed by an end plate. Further, mining augers of this type are conventionally provided with a conical end ring which is welded to the end plate. The conical end ring too, is, at its outer edge projecting towards the mining wall, provided with uniformly spaced tool holders in which cutting tool bits are arranged. These cutting tool bits project to a significant measure beyond the outer peripheral edge of the conical end ring in the direction of the mine wall. It has further been proposed to so shape the end plate that it has a frustoconical configuration when viewed cross sectionally or to provide an end plate which has a planar (radial) central part and a frustoconical part welded to the circular edge of the planar, disc-like part. In the latter case, the radially arranged disc-shaped portion of the end ring is connected with the auger shaft. The conical configuration provides that a force transmission between the mining auger and the mine wall is reduced. This improves efficiency and also reduces dust generation during operation. It has already been recognized in this connection that any deviation from a radial arrangement of the end plate leads to an improvement. It has thus been already recognized that the cone angle, that is, the angle between any line which extends radially outwardly from the auger shaft parallel with the end ring face and the axis of the auger shaft yields advantages if the angle is less than 90.degree.. Cone angles between 30.degree. and 85.degree. are conventional; a preferred cone angle range is approximately between 50.degree. and 70.degree.. Advantageous results have been achieved with a cone angle of approximately 60.degree..
It has been found in practice that the use of conical end rings substantially entirely meets the expectations. Heretofore, however, it has been a disadvantage that the service life of the conical end rings has been relatively short, presumably, because the outer circumferential zone of the conical end ring of the otherwise conical terminal body forms a frictional (scouring) edge at the mine wall; thus, this zone of the end ring is exposed to significantly large wear. This also applies to edge zones of the tool holders which are arranged in the conical end ring and which thus, similarly to the free edge zone of the conical end ring, wear extremely rapidly. Mining augers having a conical end ring and finding application in underground mining have been worn to such an extent after a few operational periods that they can no longer operate satisfactorily. It is not unusual that entire edge zones of the conical end ring break off. In addition, a substantial number of tool holders disappear entirely from the edge zone. In such cases the damaged mining augers can be repaired only by cutting off the old conical end ring by a welding torch and replacing it with a new one, since in most cases it is simply not worthwhile to repair the damaged edge zones by welding new parts thereinto.